Nickel base alloys of improved high temperature tensile ductility

ABSTRACT

THE TENSILE DUCTILITY OF LOW CHROMIUM SUBSTANTIALLY PRECIPITATION HARDENED NICKEL-BASE ALLOYS WITHIN THE TEMPERATURE RANGE OF 600* C. 900*C. IS IMPROVED THROUGH THE INCORPORATION IN THE ALLOYS OF CONTROLLED AMOUNTS OF THORIUM AND/OR CERIUM.

Unite States US. Cl. 75--122.5 6 Claims ABSTRACT 9F THE DISCLOSURE The tensile ductility of low chromium substantially precipitation hardened nickel-base alloys within the temperature range of 600 C. to 900 C. is improved through the incorporation in the alloys of controlled amounts of thorium and/ or cerium.

The present invention is directed to nickel alloys, and is particularly addressed to the problem of improving the tensile ductility of precipitation-hardenable, cast nickelbase alloys over the temperature range of 600 C. to 900 C.

As is well known to those skilled in the art, over the past 20 years or so, demands upon research have been continuous in an effort to develop alloys and components fabricated therefrom capable of withstanding the more stringent requirement imposed by advanced designs, special applications, etc. Improvements achieved in the aircraft and related industries are particularly notable in this regard as is evident from the many innovations brought about in respect of gas turbine engines. For example, alloys for stator and rotor blades have been developed which are now capable of meeting operating conditions of high stress at elevated temperatures upwards of 980 C. to about 1100 C.

Yet, notwithstanding the extensive research efforts heretofore expended it has long been a problem in the manufacture of high-temperature nickel-base alloys, such as those suitable for steam or gas turbine applications, to obtain higher levels of ductility over the temperature range of 600 C. to 900 C., particularly while otherwise retaining satisfactory properties such as high rupture strength, creep resistance and adequate corrosion resistance. The problem has been especially marked in respect of the low-chromium alloys which also contain substantial amounts of the precipitation hardening ingredients aluminum and titanium. In particular, it has been found that these alloys generally exhibit a ductility trough between 600" C. and 900 C. which can lead to premature failure of articles and parts operating within this temperature range.

It has now been discovered that the above described tensile ductility of low chromium, substantially precipitation-hardened, cast nickel-base alloys can be improved through the incorporation of special amounts of thorium and cerium.

Generally speaking, the present invention contemplates providing precipitation-hardenable, cast nickel-base alloys having improved tensile ductility in the hardened condition and which contain, by weight, up to 10.5%, e.g., 2% to 10%, chromium; up to 20%, e.g., to 16%, cobalt;

atent 3,744,996 Patented July 10, 1973 "ice up to 25%, e.g., 7% to 21%, tungsten; up to 3% to 5% iron; up to 10%, e.g., 1% to 7%, molybdenum; from 4% to 12%, e.g., 5.5% to 10%, of titanium plus aluminum; up to 12%, e.g., 0.5% to 9%, tantalum; up to 6%, e.g., 1% to 4.5%, niobium; up to 2% or 3% vanadium; up to 1.5%, e.g., 0.05% to 1%, zirconium; up to 0.3%, e.g., 0.001% to 0.05%, boron; from 0.005% to 0.15% of thorium and/or cerium, the balance being essentially nickel. Advantageously, the alloys contain from 0.02% to 0.12%, e.g., 0.05 to 0.1%, of thorium and/or cerium and most beneficially from 0.02% to 0.07%. The alloys may also contain up to 0.5% of carbon, up to 0.5 of manganese and up to 0.3% of silicon.

Thorium and/or cerium have been added to nickelbase alloys heretofore, but insofar as we are aware, these constituents have not been proposed for the purpose of enhancing tensile ductility over the above described temperature range in low chromium, nickel-base alloys greatly hardened with aluminum and/or titanium. In addition, while the subject invention results primarily in the removal or mitigation of the above-mentioned ductility trough, im provements in ductility at other temperatures may also be observed, as well as improvements in other characteristics such as stress-rupture strength and creep properties.

In carrying the invention into practice, the alloys of the invention are normally produced by vacuum melting, for example, in a vacuum induction furnace, followed by the addition of the thorium and/or cerium and then cast, preferably in an inert atmosphere under vacuum. If desired, before the thorium or cerium addition, the alloys can be subjected to vacuum refining, for example, by vigorously agitating the molten alloy in a vacuum induction furnace for an extended period of time, e.g., from 15 to 60 minutes at a temperature of 1400 C. to 1600 C., preferably not exceeding 10 microns and more preferably not exceeding 2 microns, and thereafter admitting an inert gas, e.g., argon, to a moderate pressure, e.g., mm. mercury. The thorium and/or cerium addition is then made followed by casting of the melt.

A preferred vacuum refining operation is elfected in a vacuum induction furnace for about 30 minutes under a pressure of about 1 micron with the crucible set wholly within the furnace induction coil and being between one and two thirds filled with melt thereby to maintain vigorous agitation throughout. Thus, the upper part of the coil will be above the normal level of melt in the crucible and, when the furnace is in operation, this arrangement increases the intensity of agitation to which the melt is subject.

To illustrate the improved ductility obtained as described above, the following examples and illustrative data are given:

A 50 kg. heat was made in a 55 kg. capacity 3 k./c. vacuum induction furnace and held at 1500 C. under approximately 1 micron pressure for 30 minutes.

The heat was cast as a 10 kg. stick for remelting in conventional manner. The stick was cut into 4 kg. portions which were remelted in a 10 kg. 4 k./c. vacuum induction furnace. Thorium (0.1%) and cerium (0.05%) were added under argon at a pressure of 100 mm. of mercury to the 4 kg. melts and the resultant melt in each case was cast into a preheated refractory mold to provide suitably tapered test piece blanks. Test bars were machined from the blanks and were subjected to short 4 2. A cast alloy according to claim 1, containing from 0.2 to 0.07% of cerium.

3. A cast alloy according to claim 1 containing from 2% to chromium and from 5.5% to 10% of tita- 4.l% tantalum, 0.95% titanium, 0.75% aluminum, 5 nium plus aluminum.

0.12% zirconium, 0.019% boron, the balance essentially 4. A cast steam or gas turbine article at least a portion nickel. of which is in operation at the temperature range of 600 TABLE I Creep and stress-rupture properties at- Tensile properties at Elong., at Creep strain Elong., at Minimum Elong., at. fracture U.T.S., Stress 2 hrs. prior fracture Rupture creep rate Stress Rupture fracture Addition (percent) (percent) (11. bar) (h. bar) to (tracture) (percent) lite (h.) (percent/h.) (11. bar) hie (11.) (percent) percen l Analyzed content 0.085% Th. 1 Analyzed content 0.04% Ce.

As can be seen from the data in Table I, thorium and cerium are both quite efiective in improving the 760 C. tensile ductility. For applications at temperatures above 900 C., the use of thorium does not result in the degree of loss occasioned by cerium. Thus, it is to advantage that the alloys contain thorium.

Examples of other alloys for which the tensile ductility can be improved by the addition of thorium and/or cerium in accordance with the invention are given in the following Table 11:

TABLE II Alloy, percent Al Zr B NI 5. 8 0. 14 0. 015 Balance. 6. 7 O. 13 0. 018 Do. 6. 5 0. 10 0.012 Do. 6. 3 0 l2 0. 018 Do. 5.5 0. 05 0. 018 Do. 5. 75 0. 0. 03 Do. 6. 0 0. 05 0. 10 Do.

Castings produced from the alloys in accordance herewith can be employed in automotive and aircraft turbine engine blades, and also as dies, turbine rotors, etc., particularly within the temperature range of 600 C.-900 C. and particularly with regard to cast low chromium, highly precipitation hardened nickel-base alloys. Where necessary, the chromium content can be extended to 14.5%.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understood. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A cast alloy having improved tensile ductility over the range of 600 C. to 900 C. and consisting essentially of up to 10.5% chromium, from 4% to 12% in total of titanium plus aluminum, up to 20% cobalt, up to 25% tungsten, up to 10% molybdenum, up to 12% tantalum, up to 6% niobium, up to 5% iron, up to 3% vanadium, up to 1.5% zirconium, up to 0.5% carbon, up to 0.5% manganese, up to 0.3% boron, from 0.2% to 0.15% of balance being essentially nickel.

sisting essentially of up to 14.5% chromium, from 4% to 12% in total of titanium plus aluminum, up to 20% cobalt, up to 25% tungsten, up to 10% molybdenum, up to 12% tantalum, up to 6% niobium, up to 5% iron, up to 3% vanadium, up to 1.5% zirconium, up to 0.5% carbon, up to 0.5% manganese, up to 0.3% boron, from 0.02% to 0.15% of thorium plus cerium whereby said tensile ductility is enchanced, the balance being essentially nickel.

References Cited UNITED STATES PATENTS 2,174,919 10/1939 Kay -171 X 2,432,149 12/1947 Grifliths et a1. 75171 UX 3,310,399 3/1967 Baldwin 75171 OTHER REFERENCES Chemical Abstracts, vol. 62, No. 2.555e, 1965. Chemical Abstracts, vol. 63, No. 6,677e, 1965. Chemical Abstracts, vol. 63, No. 12,805h, 1965.

CARL D. QUARFORTH, Primary Examiner R. E. SCHAFER, Assistant Examiner U.S. C1. X.R. 75-170, 171

g gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECT-ION Patent No. 3,744,996 Dated July 10, 1973 fituart Walter Ker Shaw and Paul Isidore Fontaine It is certified that error appears in the above-identified Patent and that said Letters Patent are hereby corrected as shown below:

Column 2, Erie 1, forv 3% to 5 read "3% or 5%";

Claim 1; 1% m tar 0.2%" fetid "6.82

Claim 2, line 2 for O 2%" read "0.02%"

Signed and sealed this 27th day of November 1973.

[SEALl Attest;

EDWARD M.'FLETCHER,JR. RENE D.- TEGTMEYER Acting Commissioner of Patents Attesting Office r.

25333 UNITED STATES PATENT OFFICE CERTIFICATE @F CQRREQTION Patent No. ,744,996 Dated July 10, 1973 fituart Walter Ker Shaw and Paul Isidore Fontaine It is certified that error appeare in the wove-identified patent and that said Letters latent are hereby corrected as shown below:

Column 2, line 1, for 3% to 5%" read "3% or 5%";

Claim 1, line 8, for "(1.2%" read "6.02%";

Claim 2, line 2, for "0.2%" read "0.02

(SEAL) Attest;

EDWARD MpFLETCHE'RJR. RENE D TEGTMEY'ER Acting Commissioner of Patents Attesting Officer. 

